1. Field of the Invention
The present invention relates generally to methods of use of a composition comprising hops extracts or derivatives thereof, wherein the compositions can inhibit expression of cyclooxygenase-2 (COX-2), inhibit synthesis of prostaglandins selectively in target cells, and/or inhibit inflammatory response selectively in target cells.
2. Description of the Related Art
Cyclooxygenase (prostaglandin endoperoxide synthase, EC 1.14.991, COX) catalyzes the rate-limiting step in the metabolism of arachidonic acid to prostaglandin H2 (PGH2), which is further metabolized to various prostaglandins, prostacyclin and thromboxane A2 (c.f. FIG. 1). In the early 1990s, it was established that COX exists in two isoforms, commonly referred to as COX-1 and COX-2. It was subsequently determined that the COX-1 and COX-2 proteins are derived from distinct genes that diverged well before birds and mammals. Prostaglandins (PGs) generated via the COX-1 and COX-2 pathways are identical molecules and therefore have identical biological effects. COX-1 and COX-2, however, may generate a unique pattern and variable amounts of eicosanoids; therefore, relative differences in the activation of these isozymes may result in quite dissimilar biological responses. Differences in the tissue distribution and regulation of COX-1 and COX-2 are now considered crucial for the beneficial as well as adverse effects of COX inhibitors.
The generally held concept (COX dogma) is that COX-1 is expressed constitutively in most tissues whereas COX-2 is the inducible enzyme triggered by pro-inflammatory stimuli including mitogens, cytokines and bacterial lipopolysaccharide (LPS) in cells in vitro and in inflamed sites in vivo. Based primarily on such differences in expression, COX-1 has been characterized as a housekeeping enzyme and is thought to be involved in maintaining physiological functions such as cytoprotection of the gastric mucosa, regulation of renal blood flow, and control of platelet aggregation. COX-2 is considered to mainly mediate inflammation, although constitutive expression is found in brain, kidney and the gastrointestinal tract. Therefore, it would be desirable to down-regulate tissue-specific or cell-specific expression of COX-2.
Arachidonic acid serves as the primary substrate for the biosynthesis of all PGs. PGs are ubiquitous hormones that function as both paracrine and autocrine mediators to affect a myriad of physiological changes in the immediate cellular environment. The varied physiological effects of PGs include inflammatory reactions such as rheumatoid arthritis and osteoarthritis, blood pressure control, platelet aggregation, induction of labor and aggravation of pain and fever. The discovery 30 years ago that aspirin and other non-steroidal analgesics inhibited PG production identified PG synthesis as a target for drug development. There are at least 16 different PGs in nine different chemical classes, designated PGA to PGI. PGs are part of a larger family of 20-carbon-containing compounds called eicosanoids; they include prostacyclins, thromboxanes, and leukotrienes. The array of PGs produced varies depending on the downstream enzymatic machinery present in a particular cell type. For example, endothelial cells produce primarily PGI2, whereas platelets mainly produce TXA2.
Prostaglandins (PG) are believed to play an important role in maintenance of human gastric mucosal homeostasis. Current dogma is that COX-1 is responsible for PG synthesis in normal gastric mucosa in order to maintain mucosal homeostasis and that COX-2 is expressed by normal gastric mucosa at low levels, with induction of expression during ulcer healing, following endotoxin exposure or cytokine stimulation. It now appears that both COX-1 and COX-2 have important physiological roles in the normal gastric mucosa.
Compounds that inhibit the production of PGs by COX have become important drugs in the control of pain and inflammation. Collectively these agents are known as non-steroidal anti-inflammatory drugs (NSAIDs) with their main indications being osteoarthritis and rheumatoid arthritis. However, the use of NSAIDs, and in particular aspirin, has been extended to prophylaxis of cardiovascular disease. Over the last decade, considerable effort has been devoted to developing new molecules that are direct inhibitors of the enzymatic activity of COX-2, with the inference that these compounds would be less irritating to the stomach with chronic use. Therefore, it would be desirable to inhibit inflammation response selectively in target cells.
U.S. patent application 2002/0086070A1 of Kuhrts entitled, “ANTI-INFLAMMATORY AND CONNECTIVE TISSUE REPAIR FORMULATIONS” describes a hops component that has an IC50-WHMA COX-2/COX-1 ratio ranging from about 0.23 to about 3.33. Example 1 of the application describes a composition containing an extract obtained through supercritical carbon dioxide extraction of whole hops (CO2-extract) comprising 42% humulone.
U.S. Pat. No. 6,391,346 entitled, “ANTI-INFLAMMATORY, SLEEP-PROMOTING HERBAL COMPOSITION AND METHOD OF USE” describes an orally administered composition capable of reducing inflammation in animals, while promoting sleep for such animals. The composition contains hydroalcoholic extract of hops and supercritical carbon dioxide extract of hops which are used to promote sleep.
An ideal formulation for the treatment of inflammation would inhibit the induction and activity of COX-2 without inhibiting the synthesis of PGE2 in gastric mucosal cells. However, conventional non-steroidal anti-inflammatory drugs lack the specificity of inhibiting COX-2 without affecting gastric PGE2 synthesis and are at risk to cause damages on the gastrointestinal system, when used for extended periods. Indeed, even the newly developed, anti-inflammatory drugs such as rofecoxib and celexocib produce untoward gastric toxicity in the form of induced spontaneous bleeding and delay of gastric ulcer healing.
Thus, it would be useful to identify a formulation of compounds that would specifically inhibit or prevent the synthesis of prostaglandins by COX-2 with little or no effect on synthesis of PGE2 in the gastric mucosa. Such a formulation, which would be useful for preserving the health of joint tissues, for treating arthritis or other inflammatory conditions, has not previously been discovered. The term “specific or selective COX-2 inhibitor” was coined to embrace compounds or mixtures of compounds that selectively inhibit COX-2 over COX-1. However, while the implication is that such a calculated selectivity will result in lower gastric irritancy, unless the test materials are evaluated in gastric cells, the term “selective COX-2 inhibitor” does not carry assurance of safety to gastrointestinal cells. Only testing of compound action in target tissues, inflammatory cells and gastric mucosal cells, will identify those agents with low potential for stomach irritation.
The major problem associated with ascertaining COX-2 selectivity (i.e. low gastric irritancy) is that differences in assay methodology can have profound effects on the results obtained. Depicted in Table 1 are the categories of the numerous in vitro assays that have been developed for testing and comparing the relative inhibitory activities of NSAID and natural compounds against COX-1 and COX-2. These test systems can be classified into three groups: (1) systems using animal enzymes, animal cells or cell lines, (2) assays using human cell lines, or human platelets and monocytes, and (3) currently evolving models using human cells that are representative of the target cells for the anti-inflammatory and adverse effects of NSAID and dietary supplements. Generally, models using human cell lines or human platelets and monocytes are the current standard and validated target cell models have not been forthcoming. A human gastric cell line capable of assessing potential for gastric irritancy is a need.
TABLE 1Classification of test systems for in vitro assays assessing COX-2selectivity of anti-inflammatory compounds†TEST SYSTEMSANIMALHUMANTARGETEnzymesEnzymesHuman Gastric Mucosa CellsCellsCellsHuman ChondrocytesCell linesCell linesHuman SynoviocytesOTHER SYSTEM VARIABLES1.Source of arachidonic acid - endogenous or exogenous;2.Various expression systems for gene replication of COX-1 andCOX-2;3.The presence or absence of a COX-2 inducing agent;4.COX-2 inducing agents are administered at different concentrationsand for different periods of time;5.Duration of incubation with the drug or with arachidonic acid;6.Variation in the protein concentration in the medium.†Adapted from Pairet, M. and van Ryn, J. (1998) Experimental models used to investigate the differential inhibition of cyclooxygenase-1 and cyclooxygenase-2 by non-steroidal anti-inflammatory drugs. Inflamm. Res 47, Supplement 2S93-S101 and incorporated herein by reference.
The enzymes used can be of animal or human origin, they can be native or recombinant, and they can be used either as purified enzymes, in microsomal preparations, or in whole-cell assays. Other system variables include the source of arachidonic acid. PG synthesis can be measured from endogenously released arachidonic acid or exogenously added arachidonic acid. In the later case, different concentrations are used in different laboratories.
Second, there are various expression systems for gene replication of recombinant COX-1 and COX-2 enzymes. In addition, the cells transfected with the Cox-1 or Cox-2 gene can be of diverse origins, for instance, insect cell lines or COS cells. Third, the absence or presence of a COX-2 inducing agent can vary. Cells that are stably transfected with the recombinant enzymes express this enzyme constitutively and no inducing agent is used. This is in fundamental contrast with other cells in which COX-2 has to be induced. Induction of COX-2 is commonly performed using bacterial LPS or various cytokines such as interleukin-1β or tumor necrosis factor. Additionally, these endotoxins and cytokines are administered at various concentrations.
Fourth, the duration of the incubation with the test agent, the COX-2 inducing agent, or with arachidonic acid varies among different laboratories. These differences can influence the quantitative outcome of the study, because the inhibition of COX-2 is time dependent. Finally, the protein concentration of the medium can vary; this is an issue for compounds that can bind avidly to plasma proteins.
An ideal assay for COX-2 selectivity would have the following characteristics: (1) whole cells should be used that contain native human enzymes under normal physiological control regarding expression; (2) the cells should also be target cells for the anti-inflammatory and adverse effects of the compounds; (3) COX-2 should be induced, thereby simulating an inflammatory process, rather than being constitutively expressed; and (4) PG synthesis should be measured from arachidonic acid released from endogenous stores rather than from exogenously added arachidonic acid.
Differences in methodology for can explain a dramatic difference in the results obtained for COX inhibition. For example, when assayed against the purified enzyme, ursolic acid exhibited an IC50 of 130 μM, far outside of possible physiologically obtainable concentrations [Ringbom, T. et al. (1998) Ursolic acid from Plantago major, a selective inhibitor of cyclooxygenase-2 catalyzed prostaglandin biosynthesis. J Nat Prod 61, 1212-1215]. In the RAW 264.7 murine macrophage line, Suh et al. report an IC50 for ursolic acid of approximately 40 μM [Suh, N., et al. (1998) Novel triterpenoids suppress inducible nitric oxide synthase (iNOS) and inducible cyclooxygenase (COX-2) in mouse macrophages. Cancer Res 58, 717-723]; and in phorbol 12-myristate 13-acetate stimulated human mammary cells, the approximate median inhibitory concentration of ursolic acid was 3.0 μM [Subbaramaiah, K. et al. (2000) Ursolic acid inhibits cyclooxygenase-2 transcription in human mammary epithelial cells. Cancer Res 60, 2399-2404].
No laboratory has, as yet, developed an ideal assay for COX-2 selectivity. The whole cell system most commonly used for Rx and OTC products is the human whole blood assay developed by the William Harvey Institute [Warner, T. D. et al. (1999) Nonsteroid drug selectivities for cyclo-oxygenase-1 rather than cyclo-oxygenase-2 are associated with human gastrointestinal toxicity: a full in vitro analysis. Proc Natl Acad Sci U S A 96, 7563-7568]. To date, this assay format has developed more data supporting clinical relevance than any other. However, new research in the role of constitutive expression of COX-2 in normal gastric mucosa necessitates revisiting the relevance of the use of platelets to model COX-1 inhibition in the absence of COX-2. The extrapolation of gastrotoxicity from platelet studies is no longer on a sound molecular basis. The validation of a human gastric mucosal cell line for establishing the potential target tissue toxicity of cyclooxygenase inhibitors represents a critical need for the development of safe and effective anti-inflammatory agents.
Therefore, it would be useful to identify a composition that would specifically inhibit or prevent the expression of COX-2 enzymatic activity in inflammatory cells, while having little or no effect on PGE2 synthesis in gastric mucosal cells so that these formulations could be used with no gastrointestinal upset. Furthermore, such formulations should allow for healing of pre-existing ulcerative conditions in the stomach.